This invention relates to a component for a motor vehicle air brake system, and particularly, to an air dryer desiccant cartridge.
Many motor vehicles, and in particular, heavy duty trucks incorporate air brake systems which use air pressure to control application of the vehicle service brakes. These systems have an air compressor driven by the vehicle engine which charges a brake system reservoir with high pressure air. The air compressor is controlled to supply air intermittently as needed to replenish the reservoir and maintain reservoir pressure within a predetermined range.
The process of compression of air results in the precipitation of water. Water and particulates in the air brake system can lead to component deterioration and interfere with optimal operation of the brake system. Accordingly, there are various devices used for removing water from the compressed air in air brake systems, known as air dryers. The function of an air dryer is to collect and remove air system contaminants in solid, liquid and vapor form before they enter the brake system. The air dryer provides clean, dry air for the components of the brake system which increases the life of the system and reduces maintenance costs. One type of air dryer incorporates a desiccant material which eliminates daily manual draining of water collection reservoirs as is required in other types of air dryers.
Desiccant type air dryers employ a volume of desiccant material which is hydrophilic and thus absorbs water which passes through an air line from the air compressor. High pressure air enters the desiccant air dryer and the water is stripped by the desiccant material. The air dryer also includes a particulate filter for trapping particulates and oil. Eventually, the desiccant material absorbs water to its maximum capacity. As a means of expelling this trapped water, modern desiccant type air dryers incorporate a backflow or purge air flow as a means of stripping the desiccant of absorbed water. A reservoir referred to as a purge volume is provided with is charged with the high pressure air supplied by the compressor. When the compressor cycles from a loaded mode producing compressed air to the unloaded mode, the purge volume air is allowed to leak to atmosphere through the desiccant bed in a reverse flow direction, stripping it of moisture and expelling it into the air. External purge volume air dryer types use a purge volume reservoir separate from the air dryer and connected to it by an air line. Another type is a so-called integral purge volume type in which the housing which contains a desiccant material also defines the purge volume. These types are in widespread use today and provide excellent performance.
In modern desiccant type air dryers some means of removing the desiccant material is provided since it requires rejuvenation after a service life period. In use, the desiccant material absorbs contaminants such as oil which ultimately reduces its water retention characteristics. Since other components of air dryers have a longer service life, a convenient system for removing the desiccant material is desired. In one type of air dryer, spin-on type desiccant cartridges are used. The desiccant cartridge resembles a conventional motor vehicle spin-on oil filter in a form of a canister with a load plate having a centrally threaded bore such that the entire unit is threaded onto an upstanding boss on a mounting surface. Another type of desiccant cartridge attachment system is being introduced by the assignee of the present application. In this type, a desiccant cartridge is held in place on an air dryer body assembly through threading of a through bolt which passes through a bore in the body assembly and engages threads on the load plate of the desiccant cartridge.
Air dryer desiccant cartridges are typically formed from a number of cup shaped formed sheet metal components which are assembled together and affixed to a load plate which mounts to the air dryer body assembly. A number of distinct chambers are formed in the air dryer assembly which are separated from one another. In the desiccant cartridge, a number of gaskets and elastomeric seals are provided to create the sealed areas. Designers of such articles continually strive for reduced cost and improved quality. Since the desiccant cartridge components are formed sheet metal parts, dimensional variability is also a concern. When the various components forming the desiccant cartridge are assembled, it is important that they generate the appropriate sealing engagement. Since these devices operate in an environment of intense vibration, it is further desired to avoid rattling of parts or relative movement between them. These objectives pose challenges in the design of air dryer desiccant cartridges.
In view of the foregoing, there is a continuing need to develop air dryer desiccant cartridges having improvements in manufacturability, cost and reliability and it is an object of this invention to provide such a device.